1. Field of the Invention
This invention relates generally to cardiac stimulator leads, and more particularly to method and apparatus for joining a polymeric sleeve to a tubular structure in a cardiac lead.
2. Description of the Related Art
Conventional implantable cardiac stimulator systems consist of a cardiac stimulator and one or more elongated tubular leads. The cardiac stimulator is ordinarily encased within a metallic can. The proximal ends of the leads are connected physically and electrically to the cardiac stimulator via a structure commonly known as a header. The distal end of the lead is implanted near the tissue site requiring electrical stimulation or sensing. The lead functions to carry electrical signals from the cardiac stimulator to the targeted tissue and signals from the targeted tissue back to the cardiac stimulator. The cardiac stimulator may be a pacemaker, a defibrillator, a sensing instrument, or some combination thereof.
There is great variability in the structure of conventional cardiac leads. Although some of this variety can be traced to differences in the design methodology of various lead manufacturers, many of the structural differences are simply a result of the many different types of arrhythmia therapy now possible through cardiac stimulation, such as multi-chamber pacing, defibrillation, and coronary sinus pacing, among others. However, despite the many differences in the designs of various cardiac leads, most such leads share several common structural features.
The proximal end of a typical cardiac lead, such as a bipolar lead, consists of a tubular metallic connector that is adapted to be secured to the header of a cardiac stimulator. The distal end of the lead includes one or more tubular structures that are often metallic, and may serve not only as electrodes, but may also include mechanisms to secure the lead to the targeted tissue. Electrical pathways between the proximal connector and the distal electrodes are established by one or more conductor wires extending between the proximal connector and the distal electrodes. The proximal connector and the distal electrodes are physically connected by a tubular insulating sleeve that not only physically connects the two ends of the lead, but also functions to electrically insulate the conductor wires of the lead from invasion by body fluids and tissues. Bipolar leads that incorporate non-insulated conductor wires usually include two insulating sleeves that are concentrically disposed. One of the conductor wires is disposed inside the innermost sleeve and the other wire is disposed between the first sleeve and the second sleeve.
The attachment of the sleeve(s) to the tubular structures of the proximal connector and the electrode requires a bonding between dissimilar materials, namely, the polymer sleeve to the metallic tubular structures. In conventional leads, the outer surface of the tubular structure(s) and the inner surface of the sleeve(s) are both relatively smooth. The bonding of the mating smooth surfaces is accomplished by application of a biocompatible medical grade adhesive between the surfaces. The adhesive bond is the primary mechanism to prevent the sleeve(s) from separating from the metallic tubular structures.
There are several disadvantages associated with the interconnection between the insulating sleeve and the metallic structures in conventional cardiac leads. The strength of the adhesive bond between the tubular metallic structure and the sleeve is dictated in large part by the strength of the adhesive agent, and the initial conditions of the exterior of the tubular structure and the interior of the insulating sleeve. Surface contaminants on the exterior of the tubular structure or the interior of the insulating sleeve may prevent the adhesive from bonding properly, and result in a weakened joint. To avoid or reduce the risk of improper bonding due to contamination, costly surface preparation procedures must normally be undertaken prior to application of the adhesive. In a commonly followed procedure, the metallic tubular structure is washed thoroughly in a mixture of isopropyl alcohol and heptane. Although immersion of the tubular structure in the cleaning agent is sometimes sufficient to adequately clean the structure, physical scrubbing by brushing or use of some other tool is often necessary to achieve an acceptable level of surface purity. The cleaning process slows manufacturing, requires the labor intensive input of skilled manufacturing workers, and employs solvents that often require specialized air handling equipment.
This invention is directed to overcoming or reducing one or more of the foregoing disadvantages.